(Hydroxyalkyl)polysiloxanes and (hydroxyalkyl)-polysiloxane resins incorporate as structural element units of the formulasiloxane-(SiRi2)—Rii—OH,where Ri is alkyl or aryl, generally methyl, and Rii is a hydrocarbon moiety which may contain or be substituted with heteroatoms and which is attached to the silicon atom in the (SiRi2) group via a carbon atom. The presence of Rii between the silicon atom and the depicted OH group has the effect that the bond attaching the OH group to the siloxane scaffold is hydrolysis stable. When the OH group is reacted with other compounds, the bond attaching the resulting products to the siloxane scaffold will likewise be hydrolysis stable.
The Rii group is in effect a structure-conferring factor which co-determines not only the properties of the (hydroxyalkyl)polysiloxane, or respectively (hydroxyalkyl)polysiloxane resin, but also the properties of descendant products obtainable using the (hydroxyalkyl)polysiloxane or respectively the (hydroxyalkyl)polysiloxane resin. It is especially the mobility of Rii as well as the organic character of Rii which influences these properties. When, for example, the mobility of Rii and/or the organic character of a (hydroxyalkyl)polysiloxane or respectively of a (hydroxyalkyl)polysiloxane resin or descendant products thereof are to be kept to a minimum, very small Rii moieties are ideal, and the choice of Rii as CH2 is especially advantageous. A further advantage of this choice for Rii is that small structural units mean lower reaction volumes for the same amount of substance of Rii-attached OH groups and hence enhanced space-time yields both in the production of (hydroxyalkyl)polysiloxanes or respectively of (hydroxyalkyl)polysiloxane resins and in the production of descendant products thereof.
(Hydroxyalkyl)polysiloxanes and (hydroxyalkyl)-polysiloxane resins where Rii is CH2 are hereinafter referred to as (hydroxymethyl)polysiloxanes and (hydroxymethyl)polysiloxane resins, respectively.
Methods for producing (hydroxyalkyl)polysiloxanes and (hydroxyalkyl)polysiloxane resins are described in the literature.
The references EP 629 648, EP 768 347, DE 101 09 842, DE 10 2004 029 259 and DE 10 2005 045 334 describe methods wherein polysiloxanes/polysiloxane resins or fillers that bear Si—OH groups are reacted with cyclic or linear compounds of the structure *[SiRi2—Rii—O—]φ*=end groups or ring closure; φ≧1). None of these references describes a method wherein Rii is CH2.
Methods for producing (hydroxymethyl)polysiloxanes and (hydroxymethyl)polysiloxane resins (Rii is CH2) are likewise described in the literature.
The references DE 1 213 406, DE 1 236 505, DE 1 251 320, DE 879 839 and DE 1 233 395 describe the production of (hydroxymethyl)polysiloxanes and of (hydroxymethyl)polysiloxane resins by reaction of (halomethyl)polysiloxanes and of (halomethyl)polysiloxane resins, respectively, with metal hydroxides (DE 1 213 406) or with (i) metal carboxylates and (ii) transesterification of the resultant (acyloxymethyl)polysiloxanes and (acyloxymethyl)polysiloxane resins with alcohols (DE 879 839; cf. production of (acyloxymethyl)-polysiloxanes and of (acyloxymethyl)polysiloxane resins by reaction of (halomethyl)polysiloxanes and of (halomethyl)polysiloxane resins, respectively, with ammonium carboxylates: DE 1 199 772, U.S. Pat. No. 2,833,802). However, the siloxane scaffold will generally undergo rearrangements under the conditions described.
DE 1 236 505 and DE 1 251 320 describe the production of (hydroxymethyl)polysiloxanes and of (hydroxymethyl)-polysiloxane resins respectively by transesterification of (acyloxymethyl)polysiloxanes and of (acyloxymethyl)-polysiloxane resins respectively with alcohols under catalysis by arylsulfonic acids. DE 1 236 505 describes inter alia a method wherein linear poly(dimethylsiloxane) (α,ω-OH-terminated) is reacted with an (acyloxymethyl)dimethylethoxysilane, and the Si-(acyloxymethyl) groups are transesterified with methanol to Si-(hydroxymethyl) groups (Si—CH2—OH) (reaction “f)” in DE 1 236 505). However, drastic conditions (toluenesulfonic acid and heating) have to be used to transesterify the Si-(acyloxymethyl) groups. Yet under such conditions the siloxane scaffold will generally become rearranged.
DE 1 233 395 describes the production of (hydroxymethyl)polysiloxanes and of (hydroxymethyl)-polysiloxane resins by reaction of (acyloxymethyl)polysiloxanes and of (acyloxymethyl)-polysiloxane resins respectively with alkali metal boronates and hydrolysis of the resultant primary product. However, alkali metal boronates are costly reagents and moreover can attack and change the siloxane scaffold.
DE 1 227 456, DE 879 839 and SU 1 512 982 describe the production of (hydroxymethyl)polysiloxanes and of (hydroxymethyl)polysiloxane resins by equilibration of, for example, 1,3-bis(hydroxymethyl)-1,1,3,3-tetramethyldisiloxane with cyclic or acyclic organopolysiloxanes. However, for such an equilibration reaction to take place it is necessary for the siloxane formation of the 1,3-bis(hydroxymethyl)-1,1,3,3-tetramethyldisiloxane to cleave. Yet the conditions under which this disiloxane bond is cleaved also cause siloxane bonds to rearrange/cleave in the organopolysiloxane which is to be converted.
What is common to the methods described for producing (hydroxymethyl)polysiloxanes and (hydroxymethyl)-polysiloxane resins is that the reaction conditions tend to cause rearrangements of the siloxane scaffold, and so the methods do not lead to defined products. Furthermore, the resulting ≡SiCH2OH groups are frequently not released quantitatively from the corresponding precursor compounds (e.g., ≡SiCH2—Oacyl or ≡SiCH2-halogen), and/or the resulting ≡SiCH2OH groups react further under the reaction conditions (e.g., with HCl to form ≡SiCH2Cl groups, with sulfuric acid to form ≡SiCH2OCH2Si≡ groups or with hydroxides to cleave the Si—C bond in SiCH2OH groups to Si—OH groups), and so the product does not have the theoretically expected number/concentration of ≡SiCH2OH groups. Furthermore, reagent residues and/or catalyst residues in the product frequently lead to rearrangement, cleavage, condensation or equilibration of the siloxane scaffold, and so the product properties of (hydroxymethyl)polysiloxanes and of (hydroxymethyl)polysiloxane resins produced by literature methods frequently change during storage. All these inventions hinder or prevent the further conversion of the (hydroxymethyl)polysiloxanes or (hydroxymethyl)polysiloxane resins obtained in the prior art into defined descendant products, it holds particularly for descendant reactions at the SiCH2OH group.